Radiation and matter: how do they play with each other?

Doctoral thesis, 2008

The propagation of radiation is affected by the presence of matter; at the same time, the physicochemical properties of matter are modified by the passage of radiation. The interplay of radiation and matter is of crucial importance in many modern applications: accelerated heavy ions, in particular, can be used in radiotherapeutical treatments of some cancers; moreover, they are present in the space radiation environment and represent a serious threat to the health of spaceship crews and to the functionality of electronic equipment on board. Quantitative predictions of the effects of radiation on matter and of matter on radiation consist often in numerical estimates obtained with transport codes, computer programs built on theoretical, semi-empirical and/or empirical models describing the microscopic processes that govern radiation-matter interaction. The validity of a transport code for a particular task depends directly on the accuracy of the models it uses. It is therefore very important to develop reliable microscopic models and demonstrate their suitability for the inclusion in transport codes. Indeed, the objects of this thesis are the development and the benchmarking of computer codes and microscopic models for the simulation of heavy-ion transport. We developed a semi-empirical model for the prediction of partial charge-changing cross sections for heavy ions, based on the experimentally verified weak-factorisation systematics. We also performed an extensive benchmark of partial charge-changing cross sections calculated with a number of nuclear-reaction event generators; the JQMD (JAERI Quantum Molecular Dynamics) event generator, in particular, was upgraded with the goal of improving its performance in soft, peripheral reactions. Finally, the utility of transport codes to real problems is demonstrated by application to actual problems in radiotherapy and radioprotection in space. Transport codes prove to be precious tools in the interpretation of controversial experimental data and in design and planning of equipment and shielding for several applications.